US 6,608,317 B1 · Charged-particle-beam (CPB)-optical systems with improved shielding against stray magnetic fields, and CPB microlithography apparatus comprising same · patentgrep

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Description7,270 words

Summary2,150 words

#This invention pertains to microlithography (transfer of an image of a pattern, defined by a reticle or mask, to a sensitive substrate using an energy beam). Microlithography is a key technique used in the manufacture of microelectronic devices such as integrated circuits, displays, and the like. More specifically, this invention pertains to microlithography performed using a charged particle beam such as an electron beam or ion beam. Even more specifically, the invention pertains to shielding components of the charged-particle-beam (CPB) optical system, as used in CPB microlithography apparatus, against external magnetic fields such as stray magnetic fields generated from any of various sources such as the linear motors that actuate the stage on which the substrate is mounted during exposure.

#Charged-particle-beam (CPB) microlithography is an attractive candidate technique for achieving better pattern-transfer resolution than obtainable using current optical microlithography. One type of CPB microlithography apparatus, termed a “reduction” transfer apparatus, forms a demagnified image of a highly dense and extremely fine pattern, defined on a reticle, on a sensitive substrate (e.g., resist-coated wafer). In view of the required extremely high accuracy of pattern transfer performed using a reduction CPB microlithography apparatus, external stray magnetic fields must be prevented from affecting the charged particle beam. Examples of such fields include magnetic fields generated by electrical current flowing through peripheral wires or movement of conductive bodies outside the CPB-optical system of the apparatus. A notable source of such fields is the linear motors used to provide the reticle stage and wafer stage with movability in the X- and Y-directions.

#Several conventional techniques have been proposed and implemented to prevent the effects of stray magnetic fields. One technique involves lining the walls of a room, in which the CPB microlithography apparatus is located, with a material having high permeability (e.g., “Supermalloy” or Permalloy C™, which are ferromagnetic materials containing about 75% Ni). The lining magnetically shields the interior of the room from external magnetic fields. Unfortunately, with this technique, it is difficult to achieve a high magnetic-shielding ratio (ratio of internal magnetic field to external magnetic field). For example, in a room having dimensions of length 4 m, width 4 m, and height 2 m, lining the walls with Supermalloy that is 2 mm thick provides a magnetic-shielding ratio of only about ⅓. Also, creating a room having magnetically shielded walls in this manner is prohibitively costly in many instances.

Brief description of the drawings4 figures

#The foregoing and additional features of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.

#FIG. 1 is an enlarged elevational section of the lower right portion of a wafer-side electromagnetic projection lens as used in the FIG. 3 apparatus, showing components located in the vicinity of the lens.

#FIG. 2 is an enlarged elevational section of the upper right portion of a reticle-side electromagnetic projection lens as used in the FIG. 3 apparatus, showing components located in the vicinity of the lens.

Detailed description4,956 words

#The invention is described below in the context of representative embodiments. However, it will be understood that the invention is not limited to those embodiments. Also, the invention is described in the context of using an electron beam as an exemplary charged particle beam. However, it will be understood that the general principles set forth herein are applicable with equal facility to other types of charged particle beams, such as an ion beam.

#Reference is made first to FIG. 3, depicting certain general aspects of an electron-beam microlithography apparatus used for step-and-repeat projection-transfer of a pattern from a reticle to a suitable substrate (e.g., semiconductor wafer). FIG. 3 especially shows certain details of the “electron-optical system” of the apparatus, including the focusing system and a system for controlling operation of the electron-optical system.

#An electron gun 1 is situated at the extreme upstream end of the electron-optical system. The electron gun 1 emits an electron beam that propagates downstream of the electron gun generally in the direction of an “optical axis” AX (i.e., Z-direction). The electron beam propagating from the electron gun 1 to a reticle 10 is termed an “illumination beam,” and the portion of the electron-optical system arranged along the axis AX between the electron gun 1 and the reticle 10 is termed the “illumination-optical system.” The illumination-optical system comprises two condenser lenses 2, 3 that converge the illumination beam at a crossover C.O.1 situated at a blanking aperture 7.